Taxonomy Of Late Cloudina Tubular Fossils And Discussion On Sedimentary Environment Of Ediacaran In Ningqiang Area, Shaanxi Province

Cloudina is a late Ediacaran tubular fossil,with its worldwide distribution,and a relative short life span,it has become an important index fossil in the late Ediacaran period.Although Cloudina has been studied for nearly 50 years and several important advances has been made,many problems still remain.Through a systematic study of the obtained Cloudina fossils and a comparison of relevant geochemical data from the Gaojiashan and the Lijiagou sections,the author mainly have the following understandings:(1)The decoration on the surface of the Cloudina tube has nothing to do with the size of its growth.Although striking variability in funnel overlap within Cloudina tubes do exist,it is not so significantly related to the diameter of the tube,the decoration or the sparseness or tightness of laminations.(2)A newly discovered Cloudina fossils characterized by fully developed or totally absent of transverse and oblique annulations on the exterior surface of the funnels is named and described as Cloudina gaojiashanensis sp.nov.Therefore,four species namely Cloudina hartmannae ? Cloudina ningqiangensis ? Cloudina xuanjiangpingensis ? Cloudina gaojiashanensis sp.nov.might be discernable in our collections.Although Cloudina has been widely compared with the living sabellid polychaetans or cnidarians,lacking of internal structure made its classification unreliable.(3)A class of tubular fossils with smooth and undecorated tube walls and without nesting structure is found.(4)By comparing the geochemical data from the Gaojiashan section and the Lijiagou section,the depositional environment of the Lijiagou section was much deeper than that of the Gaojiashan section,and was characterized slightly lower paleo-salinity,but somewhat higher paleo-temperature and there seems no obvious fluctuation in the paleo-environments.